He may have legal grounds to sue the parents for the medical treatment. Since the fight was an intentional act, and since it didn't occur at home, I doubt any insurance coverage will be available to the parents. So, you could sue and get nothing. Unless you can show me these parents have LOTS of money - not just well, they have a car... They probably don't have cash, neither you, nor a lawyer would ever get paid. In other words, if the facts are as you say, you can sue, but you wouldn't get paid, or paid much, so why bother?
